Many chemical processes and reactions are best performed under carefully-controlled environmental conditions. In order to maintain these conditions, the chemical reaction is often carried out in a closed vessel or chamber. While the reaction is taking place, it is necessary to carefully monitor the internal temperature of the vessel so as to insure that the process is proceeding as desired or anticipated. The vessel is, therefore, typically provided with a sleeve or channel extending outwardly therefrom having a central tapered through-bore communicating with the interior of the vessel. An elongated glass thermometer may be inserted through the channel bore to permit continuous observation and monitoring of the temperature of the process in the vessel.
Such a thermometer is provided for this purpose with an integral enlarged ground glass joint along its length having a tapered configuration substantially conforming to that of the tapered bore of the vessel sleeve. Thus, when the thermometer rod is inserted into the sleeve opening, the tapered joint enlargement seats against and within the defines of said conforming opening to cooperatively form a vacuum-tight seal therebetween. The seal is effective to prevent the escape of fluid from the vessel and to enable the maintenance of the vacuum conditions therein while an immersion portion or end of the thermometer rod is immersed in the fluid within the chamber so as to permit the monitoring of the temperature of the same.
The manner in which an integral, enlarged glass joint is fabricated on the thermometer rod involves a series of time consuming, costly operations. These operations must be performed by skilled personnel who have been specially trained in the art. Moreover, several steps in the procedure require precision glass-working techniques which render the glass rod particularly susceptible to deformation which effectively destroys the thermometer's utility for its intended purpose. Thus, an additional drawback of the integral glass joint-forming procedure is a significant waste of materials upon which skilled work--expensive work--has been performed. Since ultimately the cost of this waste must be passed along to the purchaser, the result is a substantial increase in the market price of such thermometers.
The integral enlarged ground joint is formed on the glass rod prior to the performance of the manufacturing operations that result in a completed temperature measuring rod. Specifically, glass tubing is supplied to the thermometer manufacturer in long lengths. As supplied, the tubing is provided with a uniform internal passageway throughout its length and with a sight stripe of a contrasting color to enable the temperature to be read from the completed thermometer.
A selected length of such glass rod is rotated over an open flame to heat a portion of the glass. When the heated portion of the rod has reached a temperature whereby the glass is sufficiently softened to enable it to be worked, the heated portion is gathered from its ends to form an enlargement on the rod. This enlargement is then ground to a fine taper substantially conforming to that of the opening in the vessel sleeve. After the tapered joint is successfully formed on the rod, a mercury storage bulb is blown thereon and the thermometer completed in a manner well known in the art.
Clearly, the fabrication of such an enlarged ground joint of the thermometer body material itself is an involved procedure that requires the performance of a number of precise operations on the body which are particularly susceptible to damaging the body and rendering it useless as an instrument for the precision measurement of temperature. Thus, if each operation is not correctly performed, the body may be damaged, as, for example, by a slight deformation of the internal passageway or of the sight stripe. It can therefore be appreciated that despite the performance of these operations by highly skilled and trained technicians, a significant amount of waste of the materials employed and of the labors performed thereon will of necessity occur. This will have the effect of significantly increasing the overall manufacturing costs of even satisfactorily manufactured thermometers having ground glass joints formed of the thermometer body material.
The prior art fails to disclose a thermometer having a structural arrangement rendering it applicable as a functional substitute for a ground glass joint thermometer of the type heretofore discussed. For example, U.S. Pat. No. 2,525,361 to A. H. Lamb teaches the combination of a dial-type thermometer having an elongated, rod-like sensing stem, and a tubular, resilient mounting member with a central bore therethrough for slidably receiving the thermometer stem. The mounting member is provided with a circumferential groove to facilitate its permanent securement in an opening of an airplane windshield. The disclosure contemplates the removable insertion of the thermometer stem into the bore for measurement of the air temperature outside of the aircraft.
It is clear that in applications calling for the use of an aforementioned ground glass joint thermometer, the device of Lamb would make an unsatisfactory substitute. Comparable use of the Lamb combination would require the permanent securement of a suitably modified mounting member to the vessel sleeve to enable the fluid-tight or vacuum-tight insertion of a thermometer into the vessel. Furthermore, the fit between the periphery of the thermometer skin and the defines of the mounting member's central bore must be completely tight at the outset to create a vacuumtight seal therebetween. Repeated insertion and removal of the thermometer from the mounting member will act on the defines of the central bore to deform the same, and the elevated temperatures or the chemical compositions of the reacting substance in the vessel could bring about a change in the size of the mounting member's central bore, all to the effect of destroying the required vacuum-tight seal between the thermometer and the mounting member thereof.
U.S. Pat. No. 2,724,274 to R. E. Ross teaches a milk temperature indicator for baby bottles comprising the combination of a dial-type thermometer having a rod-like sensing stem and a circular supporting collar movably positioned about the thermometer stem. The supporting collar is loosely positioned over the bottle mouth to hold the thermometer stem in submerged relation to the milk in the bottle while the indicating dial is maintained above the bottle to enable the monitoring of the temperature of the milk. Ross does not teach a vacuum-tight fit between the thermometer stem and the movable supporting member, nor does it contemplate such a seal between the supporting member and the opening in the bottle atop which it is to be loosely placed. There is, in addition, no suggestion of how it could be modified to provide such a vacuum-tight seal. The Ross combination would, therefore, as was the case with Lamb, also make an unsatisfactory substitute for a rod-like thermometer having an integral enlarged ground glass joint formed of the thermometer glass along the length thereof. Thus, the prior art teaches no adequate substitute for the expensive integrally formed glass ground joint.
The aforementioned patents are exemplary of the shortcomings of the prior art.
The desideratum of the present invention is to overcome the aforedescribed problems associated with the prior art. An object of the present invention is to avoid the significant waste of time and materials involved in the fabrication of ground glass joint thermometers in the manner described which results from degradation and deformation of the thermometer rod. This wastage, which is recognized to be an inherent disadvantage of the ground glass joint fabrication process, results in higher manufacturing costs which are reflected in the cost of such thermometers to consumers.
Another object of the present invention is to provide a method for manufacturing thermometers with a separate joint equivalent to the aforedescribed ground glass joint, but having the integral ground glass joint thereon that is formed of the thermometer body while avoiding those fabricating operations involving a high risk of damage to the thermometer body.
Still another object of the invention is to provide a thermometer with a joint for use in accomplishing the aforedescribed purposes in which the joint is made separate from, rather than as a part of, the thermometer body, but which joint, whcn applied to the thermometer body becomes an integral part thereof, functioning as a substitute for the integral ground glass joint, and yet accomplishing the same purposes as the same.
Further objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred, but nonetheless illustrative embodiments in accordance with the present invention, when taken in conjunction with the accompanying drawings.